(1) Field of the Invention
This invention relates to a filter process and its device which consist of a superficial filtration by means of coating of a filter medium and a cubical filtration by use of an isosceles triangular wire.
(2) Description of the Prior Art
Generally, the term "filter" means to remove suspended impurities by passing liquid through any substance such as cloth, paper, porous porcelain or the like. It is required to increase a filtering degree in combination of a filtering paper or a network with a porous sintered metal or a fiber. In order to carry out more accurate filtration, e.g. a filter process as shown in FIG. 1 has been introduced conventionally.
A filter device A for superficial filtration comprises a cylinder body 1, a screw thread portion 2 on its outer circumference and a plurality of pores 3 perforated in a zigzag form on the outer circumference. The plurality of pores 3 are communicated with a cavity 1a of the cylinder 1. Numeral 4 is an approximately isosceles triangular wire having a base 4a, a base surface 4b and a vertical angle .alpha..
The wire 4 is wrapped up round a screw bottom 2b in such a manner that the length of the base 4a of the wire 4 is slightly smaller than a pitch P between adjacent screw crests 2a, and the vertical angle .alpha. of the wire 4 is identical with an angle .alpha. between adjacent screw threads. Then, a slit S is formed between adjacent wires 4, 4 and a filter element E is formed, through which a liquid Li containing impurities passes as shown by arrows, and a purified liquid Lo is produced. A width w of the slit S is obtained by deducting the length of the base 4a from the pitch P.
However, one disadvantage of such conventional filter method is that it is not always possible to pass some solid impurities through the filter element E because the slit S is a lengthy gap. Another disadvantage thereof is that some liquid impurities may pass through the filter element E since its passing area is large. A further disadvantage thereof is that some screw summits 2a or some screw bottom 2b may be deformed at an edge 3a where a direction of the screw thread 2 contacts an edge of each pore 3. Accordingly, the wire 4 is not always uniformly wrapped up above the plurality of pores 3, thereby the width w of the slit S may be irregular.
In FIG. 2 there is shown another conventional filter device B, in which numeral 5 is a porous stainless steel plate of 5 mm.phi. as the lowest layer, numeral 6 is a filter paper 6 disposed thereupon and numeral 7 is a resinous layer precoated on the filter paper 6. Thus, liquid impurities can be removed one after another by the resinous layer 7, the filter paper 6 and the porous stainless steel plate 5 respectively. However, most of the impurities are filtered by the resinous layer 7 and each pore of the filter paper 6 and the porous stainless steel 5 is small in diameter. Therefore, the filter paper 6 and the porous stainless steel plate 5 are susceptible of clogging, so that the durability of the filter device B is short-range. In addition, it is not available to use a scraper to prevent clogging and to carry out back-flow cleaning. Further, if the resinous layer 7 is made of powdered resins, it is difficult to recycle it, so that it will be thrown away by one time use.
The task of this invention is to remove the aforementioned disadvantages of the conventional art.